The present invention relates to fibrous monolith components capable of performing multiple functions and processes for preparing such components. More particularly, the present invention is directed to structures capable of more than one discrete function, such as those capable of bearing structural loads and mechanical stresses in service and also capable of performing non-structural functions, including strain measurement, power generation, and/or temperature measurement.
Multitask functions typically are performed using different components within a system. In other words, the system contains more than one linked component each with its own discrete function. These systems, however, contain many limitations and disadvantages due to the number and types of components required to perform the various tasks. Size and weight restrictions, material compatibility, effective linkage between components and cost, for example, all must be considered when designing systems.
A smart material is one that receives, transmits, or processes a stimulus and responds by producing a useful effect. One example of a smart material is a shape memory alloy. When perturbed from its original shape, for example through bending, a shape memory alloy is capable of returning to its original shape when subjected to certain thermal treatments. In general, a component composed of a shape memory alloy can be deformed at a relatively low temperature and upon heating to a higher temperature will return to its original shape. Examples of shape memory alloys include gold-cadmium (AuCd), iron-platinum (FePt), nickel-titanium (NiTi), nickel-aluminum (NiAl), copper-zinc-aluminum (CuZnAl), and copper-aluminum-nickel (CuAlNi). Although such smart materials are known, typically, multiple materials must still be used in a system to perform differing functions within the system.
Another example of a smart material is a component having electro-mechanical functionality. Such a component can produce an electric field when exposed to a change in dimension caused by an imposed mechanical force (piezoelectric or generator effect), or conversely, can produce mechanical deformation or a change in shape when exposed to an applied electric field (electrostrictive or motor effect). Typically, piezoelectric and/or electrostrictive ceramics are used as the basis for electro-mechanical functionality.
Examples of piezoelectric and/or electrostrictive ceramics include lead zirconate titanate (PZT), lead lanthanum zirconate titanate (PLZT), lead barium zirconate titanate (PBZT), lead stannate zirconate titanate (PSZT), lead magnesium niobate (PMN), aluminum nitride (AlN) and barium titanate. These ceramics can be manufactured in almost any given shape or size, are chemically inert, and immune to moisture and other atmospheric conditions. Moreover, these ceramics exhibit multifunctional characteristics and are used in devices including transducers, linear actuators, vibrators, switches, speakers, benders, acoustic-canceling devices, sensors and smart systems.
Use of these piezoelectric and/or electrostrictive ceramics is limited by certain disadvantages of the materials. One significant disadvantage is that the ceramics tend to be brittle and weak. Thus, tensile strength limitations are often a limiting factor in design systems utilizing these materials.
Poling of piezoelectric and/or electrostrictive ceramics is an important aspect of the manufacture of transducers. During the poling process, a strong electric field is applied to the ceramic and then removed. This results in a poling field with the same orientation as the initial electric field. The poling process, however, is a challenging task that often results in electric breakdown before the poling process is complete, thus ruining the transducer. As a result, piezoelectric/electrostrictive ceramics must be fabricated with electrodes located on the inside and the outside, thus resulting in lower poling and driving fields. However, the fabrication of complex piezoelectric and/or electrostrictive ceramic structures having electrodes located on both the inside and outside is not an easy task. Conventional methods of fabricating these complex structures are expensive and time consuming.
Accordingly, there exists a need for materials that have improved mechanical properties and are capable of performing multiple tasks (both structural and non-structural) within a system to increase system reliability, reduce system complexity, reduce costs and otherwise improve design limitations encountered heretofore with use of conventional materials. There further exists a need in the industry for low cost, versatile techniques for the fabrication of such materials, including structures having internal or embedded electrodes and sensors.
The present invention overcomes the problems encountered in conventional systems and methods of manufacture by providing materials having properties that allow the materials to be used to perform multiple tasks while providing enhanced structural benefits within a particular system. The present invention also provides methods of fabricating multifunctional ceramic structures using fibrous monolith processing technology. The present invention further provides for easy poling and low driving voltage of piezoelectric and/or electrostrictive components and reduces costs by eliminating labor and special machining, and increases development cycle and design reliability.